2-2 Neuropsychology

Module Overview11.html

Structure and Function of the Nervous System

The Nervous System

The nervous system is a complex network that controls all physical and cognitive processes. The central nervous system (CNS) includes the brain and the spinal cord. The peripheral nervous system (PNS) includes nerves reaching the body’s appendages, the cranial nerves, and all organs. The CNS is involved in all parts of the transmission of information, including reception, processing, and storage. This intricate bodily system is what makes behavior possible.

The nervous system’s activity modifies its performance. The system receives signals from the environment and sends them throughout the body to the spinal cord and the brain for processing. The information (response) is sent from the brain or the spinal cord to various body parts in response to environmental conditions. It leads to new signal pathways to modify behavior, as appropriate.

The Neuron

The neuron is the brain’s basic unit and the workhorse of all CNS functions. At the simplest level, a neuron contains:

• A cell body that houses the cell’s important life functions
• An axon that carries information toward other cells
• Dendrites that receive information from other cells

The neuron works through electrochemical mechanisms. It releases neurotransmitters (the brain’s communication chemicals). The release of neurotransmitters helps communication from one neuron to the next in the chain. Neurotransmitters trigger an action potential, or electrical signal, when they reach the next neuron. This electrical signal travels inside the neuron. Then the cycle repeats itself. The brain has dozens of neurotransmitters, but perhaps the most important ones to neuropsychology include the amines. These amines include serotonin, dopamine, norepinephrine, and acetylcholine (Stahl, 2011). Chemical communication in the brain can be from cell to cell across the synapse. Communication can also be more diffuse, which is known as volume transmission (Srivastava et al., 2022). Psychotropic medications act on the brain through volume transmission. Therefore, the process is of significant clinical importance.

The Developing Nervous System

At birth, the brain is about 25% of its adult weight. In other words, it is disproportionally large compared to the rest of a newborn’s body. At the same time, a newborn’s body is only about 5% of its adult weight. The brain is about 75% of its adult weight by age two. Pediatricians measure head circumference during this critical growth period to gauge how the brain is growing.

The brain continues to develop throughout infancy, childhood, adolescence, and even into young adulthood. However, the first two years of life are a time of dramatic change. Most neurons are created before birth and already send and receive electrochemical impulses. At birth, the brain contains many more neurons than a person needs. A process called apoptosis eliminates excessive neurons. This process can be likened to cell death prompted by genetic instruction (Stahl, 2011). These critical first couple of years are a time of rapid growth of axons, dendrites, and synapses (particularly in the cortex). It is also a time of refinement. Frequently used pathways become stronger. Unused pathways atrophy—a process known as synaptic pruning (Stiles, 2008).

The process of synaptic pruning highlights the importance of early experiences in a child’s life. Expansion and pruning occur during every aspect of an infant’s life. This process includes listening, using language, and hearing musical rhythms. It also occurs from when children experience the world around them to when they begin to understand emotions. For typical development to occur, infants must have typical early experiences that strengthen certain connections in the brain (Kohlasch et al., 2021).

Neuron proliferation and pruning take place in infancy. A critical process called myelination also occurs in infancy. Myelination develops the myelin sheath that coats the axons. This fatty layer is important to processing speed. It allows electrical signals to travel more quickly through the neuronal network. Much of this myelination occurs in the first few months of life. Think of myelin as the plastic coating (insulation) on electrical wires. The coating prevents short-circuiting and permits a better transfer of electricity. The better the coating, the better protected the current. Thus, myelination is directly related to brain efficiency. This efficiency is known cognitively as processing speed. Disorders such as multiple sclerosis are linked to myelin damage that results in physical, cognitive, and emotional symptoms.

Human development involves important brain phases of development before and after birth. Apoptosis and synaptic pruning refine the brain while other areas continue to develop. For example, the frontal lobes are not fully developed until about the mid-20s.

References

Kohlasch, K. L., Cioffredi, L.-A., Lenninger, C., Stewart, E., Vatalaro, T., Garavan, H., Graham, A., Heil, S. H., Krans, E. E., Robakis, T., Rommel, A., Sullivan, E. L., Thomason, M., & Potter, A. (2021). Factors associated with parent views about participation in infant MRI research provide guidance for the design of the Healthy Brain and Child Development (HBCD) study. Developmental Cognitive Neuroscience, 50. https://doi-org.ezproxy.snhu.edu/10.1016/j.dcn.2021.100986.

Stahl, S. M. (2011). Stahl’s essential psychopharmacology: Neuroscientific basis and practical applications (3rd ed.). Cambridge University Press.

Stiles, J. (2008). The fundamentals of brain development: Integrating nature and nurture. Cambridge, MA: Harvard University Press.

Srivastava, P., Fotiadis, P., Parkes, L., & Bassett, D. S. (2022). The expanding horizons of network neuroscience: From description to prediction and control. NeuroImage, 258. https://doi-org.ezproxy.snhu.edu/10.1016/j.neuroimage.2022.119250